In order to improve the efficiency of machining center, the device was designed of electric spindle with double cylinder and automatic clamping and releasing tool. The design was more in safety and reliability and no pollution, as compared with the electric spindle system with single cylinder or hydrocylinder of automatic clamping and releasing tool. The basic structure and working principle were introduced of the double cylinder automatic clamping and releasing tool system of spindle, and finite element simulation analysis (FEA) was carried out on the double cylider spindle by ANSYS Workbench software, and experiemnts and tests were carried out. The results show that the tool releasing force of electric spindle becomes large, and the static rigidty of spindle satifies requirements. Working speed is far below its first critical speed, effective value of vibration speed of front bearing is less than 06 mm/s and temeprature raise is less than 20 ℃, thus it verifies the rationality of the design of electric spindle.